JP7624367B2 - Digital protection relay device - Google Patents

Description

The present invention relates to a digital protective relay device that protects objects connected to a power system.

As a conventional technique, for example, there is a digital protection control device that takes in an analog signal input from a power system via an input converter, converts the taken-in analog signal to a digital signal using an A/D (Analog/Digital) converter, calculates an amplitude value from the converted digital signal, calculates the ratio of the calculated amplitude value to a preset reference amplitude value as a gain correction coefficient, and performs gain correction with the calculated gain correction coefficient (see Patent Document 1). There is also a digital protection control device that calculates the excitation impedance of an input converter that affects the input/output characteristics, and corrects the input/output characteristics from the calculated excitation impedance and a theoretical formula for the input/output characteristics (see Patent Document 2).

Japanese Patent Application Publication No. 9-149536 JP 2013-106359 A

Conventionally, analog signals input from a power system are input to a protective relay device via an input converter in order to insulate the signal from the power system and convert it to an appropriate input level. The input/output characteristics of the transformer used in this input converter differ depending on the full-scale specification, which is the specification for the maximum amplitude of the analog signal input from the power system. Therefore, even if the input/output characteristics of the transformer differ depending on the full-scale specification, errors in the input/output characteristics of the transformer are corrected by digital calculations to ensure relay accuracy in digital protective relay devices. For example, errors in the input/output characteristics of the transformer when a rated analog signal is applied to the input converter are corrected by gain correction and phase correction.

However, when the input amplitude of the analog signal is smaller than the rated input amplitude and is the minimum input amplitude for which performance is guaranteed, the magnetic flux density of the transformer is low and the excitation current of the transformer decreases, which in turn reduces the excitation impedance of the transformer and increases the current flowing to the excitation coil of the transformer while reducing the current transmitted from the input side of the transformer to the output side of the transformer, resulting in a large input/output error of the transformer. Furthermore, since the input/output characteristics of the input converter vary due to individual differences in each transformer, in order to eliminate the characteristic variation, it is necessary to measure the input/output characteristics of the transformer alone at the minimum input amplitude for which performance is guaranteed and select and use those that are within the judgment criteria. However, in this case, there is an issue of unnecessary costs being incurred for the parts cost of the transformer that falls outside the judgment criteria range during selection and the selection measurement work cost.

The object of the present invention is to correct errors in the input/output characteristics of an input converter, regardless of whether the amplitude value of an analog signal input from a power system is between the minimum and maximum values of performance guarantee.

In order to solve the above problem, the present invention provides a plurality of input converters that receive an analog signal representing an analog amount of an electrical signal from a protected object connected to a power system, convert the level of the received analog signal, and output the converted level; a plurality of analog-digital converters that convert the analog signal output from each of the input converters into a digital signal; a plurality of Fourier transform calculation units that perform Fourier transform processing on the digital signal output from each of the analog-digital converters to calculate the amplitude value and phase of each of the analog signals; a correction calculation unit that performs a calculation to correct the amplitude value calculated by each of the Fourier transform calculation units with a first correction amount and a calculation to correct the phase calculated by each of the Fourier transform calculation units with a second correction amount; a protection calculation unit that performs a protection calculation process for the protected object based on the calculation results of each of the correction calculation units; an analog-digital converter for a phase reference signal that converts a phase reference signal into a digital signal; and a phase reference signal Fourier transform calculation unit that performs the Fourier transform process on the digital signal output from the phase reference signal analog-digital converter to calculate the amplitude and phase of the phase reference signal and outputs each calculation result to the correction calculation unit. The correction calculation unit is characterized in that, under the condition that an adjustment input signal, which is an AC signal equivalent to the analog signal and is a known input signal for adjustment whose amplitude value changes sequentially in multiple steps from the low input amplitude minimum value to the rated input amplitude value of the analog signal according to the sweep step amount, is input to a specific input converter among the multiple input converters, the correction calculation unit calculates the first correction amount based on the amplitude value of the adjustment input signal among the calculation results of a specific Fourier transform calculation unit corresponding to the specific input converter among the multiple Fourier transform calculation units, and calculates the second correction amount based on the phase of the adjustment input signal among the calculation results of the specific Fourier transform calculation unit.

According to the present invention, errors in the input/output characteristics of the input converter can be corrected regardless of whether the amplitude value of the analog signal input from the power system is anywhere between the minimum and maximum values of the performance guarantee.

1 is a configuration diagram showing a configuration example of a digital protection relay device according to a first embodiment of the present invention; FIG. 1 is a configuration diagram showing an example of the hardware and software configuration of a digital protection relay device according to a first embodiment of the present invention. 11 is a flowchart for explaining a correction process when a rated input is applied in the digital protective relay device used in the comparative example. FIG. 13 is an input/output characteristic diagram of the digital protective relay device used in the comparative example, obtained by correction processing when a rated input is applied. 4 is a flowchart for explaining a first correction process at the time of a low input amplitude in the digital protection relay device according to the first embodiment of the present invention. 11 is a flowchart for explaining a second correction process at the time of a low input amplitude in the digital protection relay device according to the second embodiment of the present invention. 11 is a flowchart for explaining a process to which a second correction process result is applied at the time of a low input amplitude in a digital protection relay device according to a second embodiment of the present invention. FIG. 11 is an input/output characteristic diagram of the digital protection relay device according to the second embodiment of the present invention, when the input amplitude is low, based on the second correction process. 13 is a flowchart for explaining a third correction process of the digital protection relay device according to the third embodiment of the present invention. 13 is a flowchart for explaining a process to which a third correction process result is applied in the digital protection relay device according to the third embodiment of the present invention. FIG. 11 is an input/output characteristic diagram of the digital protection relay device according to the third correction process of the third embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1 is a configuration diagram showing an example of the configuration of a digital protection relay device according to a first embodiment of the present invention. In Figure 1, the digital protection relay device 1 includes a plurality of input converters 1a, a plurality of analog filters 1b, a plurality of A/D converters 1c, a plurality of digital filters 1d, a CPU (Central Processing Unit) 1e, a work memory 1f, a non-volatile memory for recording correction values 1g, and an input/output interface (I/O interface) 1h, and each digital filter 1d, CPU 1e, work memory 1f, non-volatile memory for recording correction values 1g, and input/output interface 1h are connected to each other via a bus 1i.

Each input converter 1a is divided into multiple channels, for example, 16 channels consisting of (three-phase/zero-phase) x (input side + output side) x (voltage + current), and is connected to the power system 10. It is composed of a transformer (VT) or current transformer (CT) that converts the voltage signal or current signal, which is an analog signal (50 Hz or 60 Hz) from the power system 10, to a voltage or current level that can be handled by an analog electronic circuit and outputs the converted voltage or current signal to each analog filter 1b. When the input converter 1a is composed of a transformer, the input converter 1a converts the voltage signal from the power system 10 to a voltage signal within the range of, for example, ±10V.

One of the multiple analog filters 1b (analog filter for phase reference signal) 1b inputs a phase reference signal 20, passes only signals in the frequency band of the input phase reference signal 20, and outputs them to an A/D converter (A/D converter for phase reference signal) 1c, while the remaining analog filters 1b input analog signals from each input converter 1a, passes only signals in the frequency band of the input analog signal, and outputs them to each A/D converter 1c. In this case, each analog filter 1b can be an analog filter for preventing aliasing errors due to digital sampling.

Each A/D converter 1c converts an analog signal into a digital signal and transfers the converted digital signal to the CPU 1e. The CPU 1e is composed of a processor that functions as a control unit that controls the entire digital protection relay device 1, and receives the output signal of each digital filter 1b via the bus 1i, as well as the correction values recorded in the non-volatile memory 1g, and executes various protection calculation processes based on the control program stored in the work memory 1f or the storage device. The work memory 1f can be a RAM (Random Access Memory), and the non-volatile memory 1g can be a conductive memory such as a flash memory.

At this time, for example, if the voltage from any one of the multiple channels changes from 100 V to 0 V, the current changes from 5 A to 20 A, and a zero-phase current is detected, the CPU 1e determines that a ground fault has occurred on that channel and executes a protection calculation process to operate a protection relay to protect the transformer to be protected.

Figure 2 is a configuration diagram showing an example of the hardware and software configuration of a digital protection relay device according to embodiment 1 of the present invention. In Figure 2, the hardware 2a of the digital protection relay device 1 is composed of an input converter 1a, multiple analog filters 1b, multiple A/D converters 1c, and a non-volatile memory 1g for recording correction values. The software 2b of the digital protection relay device 1 includes a specific Fourier transform calculation unit 2c that performs Fourier transform processing on the digital signal output from the A/D converter 1c that converts the phase reference signal 20 into a digital signal, a phase reference signal Fourier transform calculation unit 2c that performs Fourier transform processing on the digital signal output from the A/D converter 1c that converts the analog signal from the power system 10 into a digital signal, a correction calculation unit 2d that performs calculation to correct the amplitudes A0, A1 and phases θ0, θ1 of the signals Fourier transformed by each Fourier transform calculation unit 2c with each correction value (first correction amount and second correction amount) recorded in the correction value recording nonvolatile memory 1g, and generates a correction processing signal of amplitude Ac1 and phase θc1, and a protection calculation unit 2e that performs a protection calculation based on the correction processing signal based on the calculation result of the correction calculation unit 2d and judges the presence or absence of an accident (ground fault, etc.) in the power system by this protection calculation. Each calculation unit is configured by a control program. At this time, the correction calculation unit 2d performs a calculation to correct the amplitude value calculated by each Fourier transform calculation unit 2c with a first correction amount, and a calculation to correct the phase calculated by each Fourier transform calculation unit 2c with a second correction amount. In addition, the protection calculation unit 2e performs a calculation to detect earth faults and short circuit faults in each channel based on the calculation results of the correction calculation unit 2d. Note that FIG. 2 shows only the input converter 1a, analog filter 1b, and A/D converter 1c used for the correction calculation among the hardware 2a of the digital protection relay device 1.

Fig. 3 is a flow chart for explaining the correction process when the rated input is applied by the digital protective relay device used in the comparative example. In Fig. 3, the digital protective relay device used in the comparative example takes in the rated input amplitude A _R1 of the analog signal, the theoretical amplitude value A _T1 of the rated input, the gain correction amount G _CR1 , the rated input phase θ _R1 of the analog signal, the reference signal phase θ _REF , and the phase correction amount θ _CR1 as input information (S1), and calculates the gain correction amount G _CR1 at the rated input and the phase correction amount θ _CR1 based on the input information (S2). At this time, the gain correction amount G _CR1 at the rated input is calculated from the gain correction amount G _CR1 = the theoretical amplitude value A _T1 of the rated input / the rated input amplitude A _R1 . The phase correction amount θ _CR1 is calculated from the phase correction amount θ _CR1 = the phase correction amount θ _CR1 - the reference signal phase θ _REF .

Fig. 4 shows the input/output characteristics after correction processing when the rated input is applied for the digital protective relay device used in the comparative example. As shown in Fig. 4, in the comparative example, the gain correction amount G _CR1 and the phase correction amount θ _CR1 are calculated based on the analog signal at the rated input, so it can be seen that the error in the input/output characteristics becomes large when the input amplitude is low.

Figure 5 is a flowchart for explaining the first correction process at low input amplitude of the digital protection relay device according to the first embodiment of the present invention. This process is a correction process at low input amplitude at the time of shipment from the factory, and is a process for averaging the correction error.

In Fig. 5, for example, a specific input converter 1a shown in Fig. 2 receives an adjustment input signal, which is a known input signal for adjustment and whose amplitude value changes in multiple steps from the low input amplitude minimum value of the analog signal (minimum value for guaranteed performance, for example, several tens of _mV or several tens of mA) to the rated input amplitude value (maximum value for guaranteed performance, for example, 110 V or 5 A) in accordance with a sweep increment (low input amplitude sweep increment ΔA L , for example, 0.1 V). The adjustment input signal is a signal that changes in multiple steps, for example, from several tens of mV to 110 V, in increments of 0.1 V. Note that performance assurance means guaranteeing the performance of the digital protective relay device 1.

The correction calculation unit 2d starts processing (S11) with respect to information related to the low input amplitude A _L [i], low input amplitude theoretical value A _LT [i], low input gain correction amount G _CL [i], low input phase θ _L [i], reference signal phase θ _REF [i], low input phase correction amount θ _CL [i], low input gain average correction amount G _AVL , low input phase average correction amount θ _AVL , low input amplitude sweep increment ΔA _L and rated input amplitude A _R1 . At this time, the correction calculation unit 2d processes as (A _R1 -A _L )/ΔA _L =N (N is a natural number), A _L [i] =A _R1 , i = 0, A _L [0] = low input amplitude minimum value.

When an adjustment input signal is input to a specific input converter 1a, the correction calculation unit 2d receives each calculation result of the specific Fourier transform calculation unit 2c corresponding to the specific input converter 1a and each calculation result of the phase reference signal Fourier transform calculation unit 2c, and calculates a low input gain correction amount G _CL [i] for the amplitude value of the adjustment input signal and a low input phase correction amount θ _CL [i] for the phase of the adjustment input signal for each sweep increment (low input amplitude sweep increment ΔA _L ) (S12). At this time, the correction calculation unit 2d calculates the low input gain correction amount G _CL [i] = low input amplitude theoretical value A _LT [i] defined in the phase reference signal 20 / low input amplitude A _L [i] of the adjustment input signal, and calculates the low input phase correction amount θ _CL [i] = low input phase θ _L [i] of the adjustment input signal - reference signal phase θ _REF .

Next, the correction calculation unit 2d calculates the low input gain average correction amount G _AVL and the low input phase average correction amount θ _AVL for each sweep increment (low input amplitude sweep increment ΔA _L ) based on the calculation result of step S12 (S13). At this time, the correction calculation unit 2d calculates the low input gain average correction amount G _AVL = low input gain average correction amount G _AVL (initial value) + low input gain correction amount G _CL [i] / N, and calculates the low input phase average correction amount θ _AVL = low input phase average correction amount θ _AVL (initial value) + low input phase correction amount θ _CL [i] / N.

Then, the correction calculation unit 2d executes the process of setting i = i + 1 (S14), and then judges whether i is smaller than N or equal to N (S15). If i is smaller than N or equal to N, the process proceeds to step S12 and the processes of steps S12 to S15 are repeated. If i is greater than N, the process result of step S13 is stored in the non-volatile memory 1g for recording correction values (S16), and then the process of this routine ends.

By the above process, the correction calculation unit 2d calculates a gain correction amount as a first correction amount from the ratio between the average value of the amplitude theoretical value for each sweep increment specified for the phase reference signal and the amplitude value of the adjustment input signal among the calculation results of the specific Fourier transform calculation unit 2c, which is the average value of the amplitude value for each sweep increment, and calculates a phase correction amount as a second correction amount from the phase of the adjustment input signal among the calculation results of the specific Fourier transform calculation unit 2c, which is the difference between the average value of the phase for each sweep increment and the phase of the phase reference signal.

According to this embodiment, regardless of whether the amplitude value of the analog signal input from the power system is anywhere between the minimum and maximum values of the performance guarantee, the error in the input/output characteristics of the input converter can be averaged and corrected across the minimum to maximum signal range, and as a result, it is possible to obtain a gain correction amount and a phase correction amount in which the error in the input/output characteristics of the input converter is averaged and corrected across the minimum to maximum signal range.

Figure 6A is a flowchart for explaining the second correction process at low input amplitude of the digital protection relay device according to the second embodiment of the present invention. This process is a correction process at low input amplitude at the time of shipment from the factory, and calculates the correction error by linear approximation using the least squares method. Note that the hardware and software configurations of the digital protection relay device in the second embodiment are the same as those in the first embodiment.

In FIG. 6A, for example, a specific input converter 1a shown in FIG. 2 receives an adjustment input signal that changes in multiple steps of 0.1 V from several tens of mV to 110 V, as in the case of Example 1.

The correction calculation unit 2d starts processing on information related to the low input amplitude A _L [i], the low input amplitude theoretical value A _LT [i], the low input gain correction amount G _CL [i], the low input phase θ _L [i], the reference signal phase θ _REF [i], the low input phase correction amount θ _CL [i], the low input gain correction amount calculated value G _Lcalc , the low input phase correction amount calculated value θ _Lcalc , the low input amplitude sweep increment ΔA _L , and the rated input amplitude A _R1 (S21). At this time, the correction calculation unit 2d processes as (A _R1 -A _L )/ΔA _L =N (N is a natural number), A _L [i] =A _R1 , i = 0, and A _L [0] = the low input amplitude minimum value (S21).

Next, the correction calculation unit 2d calculates a low input gain correction amount G _CL [i] from the low input amplitude theoretical value A _LT [i] defined in the phase reference signal 20 and the low input amplitude A _L [i] of the adjustment input signal, and also calculates a low input phase correction amount θ _CL [i] from the low input phase θ _L [i] of the adjustment input signal and the reference signal phase θ _REF of the phase reference signal 20 (S22). At this time, the correction calculation unit 2d calculates the low input gain correction amount G _CL [i] = low input amplitude theoretical value A _LT [i] / low input amplitude A _L [i], and calculates the low input phase correction amount θ _CL [i] = low input phase θ _L [i] - reference signal phase θ _REF .

Then, the correction calculation unit 2d executes the process of setting i = i + 1 (S23), and then judges whether i is smaller than N or equal to N (S24). If i is smaller than N or equal to N, the process proceeds to step S22, and the processes of steps S22 to S24 are repeated. If i becomes larger than N, the loop count i is reinitialized as i = 0 (S25).

By the processing of steps S22 to S24, the correction calculation unit 2d calculates a low input gain correction amount G _{CL [i] for each sweep increment (low input amplitude sweep increment ΔA L ) from the low input amplitude theoretical value A LT [i] of the phase reference signal 20 and the low input amplitude A L [i] of the adjustment input signal, and calculates a low input phase correction amount θ CL [i] for each sweep increment (low input amplitude sweep increment ΔA L ) from the} low input phase θ _L [i] of the adjustment input _signal and the reference signal phase θ _REF of the phase reference signal 20.

Next, the correction calculation unit 2d calculates gain correction approximate line calculation coefficients Yg, Xg _, Xgsq, XYg and phase correction approximate line coefficients Yp, Xp, Xpsq, XYp using the approximate lines of gain correction and phase correction as coefficients of linear approximation by the least squares method based on the calculation results of steps S22 to S24 (S26). At this time, the correction calculation unit 2d calculates the gain correction approximate line calculation coefficient Xg = Xg (initial value) + low input amplitude A _L [i], calculates the gain correction approximate line calculation coefficient Yg = Yg (initial value) + low input gain correction amount G _CL [i], calculates the gain correction approximate line calculation coefficient Xgsq = Xgsq (initial value) + low input amplitude A _L [i] × low input amplitude A _L [i], and calculates the gain correction approximate line calculation coefficient XYg = XYg (initial value) + low input amplitude A _L [i] × low input gain correction amount G _CL [i]. In addition, the correction calculation unit 2d calculates the phase correction approximate straight-line coefficient Xp as Xp (initial value) + low input amplitude A _L [i], the phase correction approximate straight-line coefficient Yp as Yp (initial value) + low input phase correction amount θ _CL [i], the phase correction approximate straight-line coefficient Xpsq as Xpsq (initial value) + low input amplitude A _L [i] × low input amplitude A _L [i], and the phase correction approximate straight-line coefficient XYp as XYp (initial value) + low input amplitude A _L [i] × low input gain correction amount G _CL [i].

Then, the correction calculation unit 2d executes the process of setting i = i + 1 (S27), and then judges whether i is smaller than N or equal to N (S28). If i is smaller than N or equal to N, the process proceeds to step S26 and repeats the processes of steps S26 to S28. If i is greater than N, the process proceeds to step S29.

Next, the correction calculation unit 2d calculates the slope _aG and intercept _bG of the gain correction approximate line at the low input amplitude A _L , and the slope _aθ and intercept _bθ of the phase correction approximate line based on the calculation results of steps S26 to S28, calculates a low input gain correction amount calculation value G _Lcalc from the calculation result (gain correction approximate line equation), and calculates a low input phase correction amount calculation value θ _Lcalc from the calculation result (phase correction approximate equation) (S29), and then terminates the processing of this routine.

At this time, the correction calculation unit 2d calculates the slope _aG of the gain correction approximate line as (N×XYg-Xg×Yg)/(N×Xgsq-Xg×Xg), calculates the intercept _bG of the gain correction approximate line as (Yg×Xgsq-Xg×XYg)/(N×Xgsq-Xg×Xg), and calculates the slope _aθ of the phase correction approximate line as (N×XYp-Xp×Yp)/(N×Xgsq-Xg×Xp), and calculates the intercept _bθ of the phase correction approximate line as (Yp×Xpsq-Xp×XYp)/(N×Xpsq-Xg×Xp).

Furthermore, the correction calculation unit 2d calculates the low input gain correction amount calculated value G _Lcalc as = slope a _G of the gain correction approximate line × low input amplitude A _L + intercept b _G of the gain correction approximate line, and calculates the low input phase correction amount calculated value θ _Lcalc as = slope a _θ of the phase correction approximate line × low input amplitude A _L + intercept b _θ of the phase correction approximate line, and stores the calculated low input gain correction amount calculated value G _Lcalc as the first correction amount and the low input phase correction amount calculated value θ _Lcalc as the second correction amount in the correction value recording non-volatile memory 1g.

Figure 6B is a flowchart for explaining the process of applying the second correction process result at low input amplitude in the digital protection relay device according to the second embodiment of the present invention.

6B, for example, an analog signal is input to each input converter 1a. The correction calculation unit 2d inputs information on the input amplitude A _in of the analog signal, the input phase θ _in of the analog signal, the rated amplitude A _R of the analog signal, the low input amplitude A _L of the analog signal, the rated gain correction amount G _CR1 of the analog signal, and the rated phase correction amount θ _CR1 of the analog signal, as well as information on the low input gain correction amount calculation value G _Lcalc and the low input phase correction amount calculation value θ _Lcalc calculated in step S29, and starts a process of calculating an intermediate amplitude value A _MID =(A _R +A _L )/2 between the rated input amplitude A _R and the low input amplitude A _L , the corrected amplitude A _out , and the corrected phase θ _out based on the input information (S31).

Next, when the correction calculation unit 2d calculates the intermediate amplitude value A _MID = (A _R + A _L ) / 2 between the rated input amplitude A _R of the analog signal and the low input amplitude A _L of the analog signal, it judges whether the input amplitude A _in is larger than the intermediate amplitude value A _MID (S32), and when it judges that the input amplitude A _in is larger than the intermediate amplitude value A _MID , it calculates the corrected amplitude A _out and the corrected phase θ _out (S33), and then ends the processing of this routine. At this time, the correction calculation unit 2d calculates the corrected amplitude A _{out =} input amplitude A _in × rated gain correction amount G _CR1 , and the corrected phase θ _out = input phase θ _in × rated phase correction amount θ _CR1 .

The correction calculation unit 2d calculates a corrected _amplitude A out (first corrected amplitude ₎ from the input amplitude A _in of the analog signal and the rated gain correction amount G _CR1 , and calculates a corrected phase θ _out (first corrected phase) from the input phase θ _in of the analog signal and the rated phase correction amount θ _CR1, provided that the input amplitude A _in is greater than the intermediate amplitude value A MID, corrects the amplitude value of the analog signal calculated by the Fourier transform calculation unit 2c based on the calculated first corrected amplitude, and corrects the phase of the analog signal calculated by the Fourier transform calculation unit 2c based on the calculated first corrected phase.

On the other hand, if it is determined in step S32 that the input amplitude _Ain is smaller than the intermediate amplitude value A _MID , the correction calculation unit 2d determines whether the input amplitude _Ain satisfies the condition 0≦ _Ain <A _MID (S34). If it is determined that the input amplitude _Ain is between 0 and the intermediate amplitude value A _MID , the correction calculation unit 2d calculates the corrected amplitude _Aout and the corrected phase _θout (S35), and then ends the processing in this routine. At this time, the correction calculation unit 2d calculates the corrected amplitude Aout ₌ input amplitude _Ain × low input gain correction amount calculated value _GLcalc , and the corrected phase θout ₌ input phase _θin × low input phase correction amount calculated value _θLcalc .

The correction calculation unit 2d calculates a corrected amplitude A _{out ( second} corrected amplitude ₎ from the input amplitude A _in of the analog signal and the low input gain correction amount calculation value G _Lcalc , and calculates a corrected phase θ _out (second corrected phase) from the input phase θ _in of the analog signal and the low input phase correction amount calculation value θ _Lcalc , provided that the input amplitude A in of the analog signal is in the range of 0≦A in <A MID, and _corrects the amplitude value of the analog signal calculated by the Fourier transform calculation unit 2c based on the calculated second corrected amplitude, and corrects the phase of the analog signal calculated by the Fourier transform calculation unit 2c based on the calculated second corrected phase.

Furthermore, if the correction calculation unit 2d determines in step S34 that the input amplitude _Ain does not satisfy the condition 0≦ _Ain < _AMID , it detects an abnormality in the amplitude value (S36), and then terminates the processing in this routine.

Figure 7 shows the input/output characteristics of the digital protection relay device according to the second embodiment of the present invention when the input amplitude is low, using the second correction process. In this embodiment, when the input amplitude is low, the correction error is calculated using a linear approximation based on the least squares method, and as shown in Figure 7, it can be seen that the error when the input amplitude is low is smaller than that of the comparative example shown in Figure 4.

According to this embodiment, regardless of whether the amplitude value of the analog signal input from the power system is anywhere between the minimum value and the maximum value of the performance guarantee, the error of the input/output characteristics of the input converter over the signal range from the minimum value to the maximum value can be corrected by the calculation of the linear approximation by the least squares method, and as a result, it is possible to obtain the gain correction amount and the phase correction amount corrected by the linear approximation by the least squares method. Also, according to this embodiment, the amplitude value of the analog signal input from the power system can be corrected by dividing into a case where the input amplitude _Ain is between 0 and the intermediate amplitude value A _MID and a case where the input amplitude _Ain is larger than the intermediate amplitude value A _MID .

Figure 8A is a flowchart for explaining the third correction process of the digital protection relay device according to the third embodiment of the present invention. This process involves sweeping and inputting a known input signal (adjustment input signal) for adjustment, which varies from the minimum input amplitude that guarantees the performance of the digital protection relay device according to the present invention to the full-scale input amplitude, which is the maximum amplitude, and creating a lookup table of gain correction values and phase correction values corresponding to the input amplitude of the input adjustment input signal. Note that the hardware and software configurations of the digital protection relay device in the third embodiment are the same as those in the first embodiment.

In FIG. 8A, for example, an adjustment input signal that changes sequentially in multiple steps of 0.1 V from several tens of mV to 110 V is input to the specific input converter 1a shown in FIG. 2, as in the case of Example 1.

The correction calculation unit 2d starts processing on information related to the input amplitude A[i] of the adjustment input signal, the input amplitude theoretical value A _T [i] defined in the phase reference signal 20, the input gain correction amount G _C [i], the input phase θ[i] of the adjustment input signal, the reference signal phase θ _REF [i] of the phase reference signal 20, the input phase correction amount θ _C [i], and the full-scale input amplitude A _FS of the adjustment input signal, and executes processing to initialize the input amplitude sweep increment ΔA as (A _FS -A[0])/ΔA=N (N is a natural number), A[N]=A _FS , i=0, and A[0]=low input amplitude minimum value (S41).

Next, the correction calculation unit 2d calculates the input gain correction amount G _C [i] of the adjustment input signal and the input phase correction amount θ _C [i] of the adjustment input signal based on the calculation results of each Fourier transform calculation unit 2c (S42). At this time, the correction calculation unit 2d calculates the input gain correction amount G _C [i] = the input amplitude theoretical value A _T [i] defined in the phase reference signal 20 / the input amplitude A[i] of the adjustment input signal, and calculates the input phase correction amount θ _C [i] = the input phase θ[i] of the adjustment input signal - the reference signal phase θ _REF of the phase reference signal 20.

Next, the correction calculation unit 2d records the input gain correction amount G _C [i] corresponding to the input amplitude A[i] in the gain correction lookup table GLLUT as a first correction amount, and records the input phase correction amount θ _C [i] corresponding to the input amplitude A[i] in the phase lookup table PLUT as a second correction amount (S44), as a process of recording a gain correction lookup table that outputs an input gain correction amount G _C [i] corresponding to the input amplitude A[i] and a phase correction lookup table that outputs an input phase correction amount θ _C [i] corresponding to the input amplitude A[i]. Note that the gain correction lookup table GLLUT and the phase lookup table PLUT are stored in the correction value recording nonvolatile memory 1g.

Then, the correction calculation unit 2d executes the process of setting i = i + 1 (S44), and then judges whether i is smaller than N or equal to N (S45). If i is smaller than N or equal to N, the process proceeds to step S42, and the processes of steps S42 to S45 are repeated. If i becomes larger than N, the process of this routine ends.

The correction calculation unit 2d calculates an input gain correction amount corresponding to each sweep increment as a gain correction amount from the ratio between the amplitude theoretical value for each sweep increment specified for the phase reference signal 20 and the amplitude value for each sweep increment (input amplitude sweep increment ΔA) of the adjustment input signal among the calculation results of the Fourier transform calculation unit 2c, and records the calculated input gain correction amount corresponding to each sweep increment as a first correction amount in the gain correction lookup table GLUT, and calculates an input phase correction amount corresponding to each sweep increment as a phase correction amount from the difference between the phase for each sweep increment and the phase of the phase reference signal among the calculation results of the Fourier transform calculation unit 2c, and records the calculated input phase correction amount corresponding to each sweep increment as a second correction amount in the phase lookup table PLUT.

Figure 8B is a flowchart for explaining the process for applying the results of the third correction process of the digital protection relay device according to the third embodiment of the present invention.

8B , for example, an analog signal is input to each input converter 1a. The correction calculation unit 2d starts processing on information relating to the input amplitude A _in of the analog signal, the input phase θ _in of the analog signal, the gain correction lookup table GLUT, the phase lookup table PLUT, the lookup table input A[i], the input gain correction amount G _C [i], the input phase correction amount θ _C [i], the corrected amplitude A _out , and the corrected phase θ _out (S51).

The correction calculation unit 2d receives information indicating the calculation results of each of the Fourier transform calculation units 2c, and calculates the look-up table input A[i] based on the input amplitude _Ain of the analog signal from the received information (S52).

Next, the correction calculation unit 2d outputs the input gain correction amount G _C [i] from the gain correction lookup table GLUT, and outputs the input phase correction amount θ _C [i] from the phase lookup table PLUT (S53).

Next, the correction calculation unit 2d calculates the corrected amplitude _Aout and the corrected phase _θout based on the information input in step S51 and the information output in step S53, and then ends the processing of this routine. At this time, the correction calculation unit 2d calculates the corrected amplitude _Aout = input amplitude _Ain × input gain correction amount G _C [i], and calculates the corrected phase _θout = input phase _θin - input phase correction amount θ _C [i].

When an analog signal whose amplitude value includes one of the sweep increments (input amplitude sweep increment ΔA) is input to each input converter 1a, the correction calculation unit 2d extracts an input gain correction amount corresponding to the sweep increment specified by the amplitude value of the analog signal from the gain correction lookup table GLUT, corrects the amplitude value of the analog signal calculated by the Fourier transform calculation unit 2c based on the extracted input gain correction amount, extracts an input phase correction amount corresponding to the sweep increment specified by the amplitude value of the analog signal from the phase lookup table PLUT, and corrects the phase of the analog signal calculated by the Fourier transform calculation unit 2c based on the extracted input phase correction amount.

Figure 9 shows an input/output characteristic diagram of the third correction process of the digital protective relay device according to the third embodiment of the present invention. In this embodiment, the adjustment input signal that changes from the minimum input amplitude that guarantees the performance of the digital protective relay device to the full-scale input amplitude, which is the maximum amplitude, is swept, and the error of the input/output characteristic of the input converter is corrected over the signal range from the minimum value to the maximum value. As a result, as shown in Figure 9, the input/output characteristic shows a smaller error in the entire range from low input amplitude (minimum input) to rated input amplitude (full-scale input) than that of the comparative example shown in Figure 4.

According to this embodiment, even if the amplitude value of the analog signal input from the power system is anywhere between the minimum and maximum values of the performance guarantee, it is possible to obtain a gain correction amount and an input phase correction amount in which the error of the input/output characteristics of the input converter is corrected across the minimum to maximum signal range. For example, even if an analog signal ranging from a low input signal range of tens of mA and tens of mV to a high input signal range of full scale is input to the input converter, it is possible to obtain an input gain correction amount and an input phase correction amount in which the error of the input/output characteristics of the input converter is corrected across the low to high input signal range. As a result, it is possible to realize a digital protection relay device that ensures a dynamic range for the analog signal from the power system.

The present invention is not limited to the above-described embodiments, but includes various modifications and equivalent configurations within the spirit of the appended claims. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the configurations described.

Furthermore, each of the configurations, functions, etc. described above may be realized in part or in whole in hardware, for example by designing them as integrated circuits, or in software, by a processor interpreting and executing a program that realizes each function.

Information such as programs, tables, and files that realize each function can be stored in a storage device such as a memory, a hard disk, or an SSD (Solid State Drive), or in a recording medium such as an IC (Integrated Circuit) card, an SD card, or a DVD (Digital Versatile Disc).

1 Digital protection relay device, 1a Input converter, 1b Analog filter, 1c A/D converter, 1d Digital filter, 1e CPU, 1f Work memory, 1g Non-volatile memory, 1h Input/output interface, 1i Bus, 2a Hardware, 2b Software, 2c Fourier transform calculation unit, 2d Correction calculation unit, 2e Protection calculation unit

Claims (7)

A plurality of input converters that receive analog signals representing electrical signals of analog quantities from objects to be protected that are connected to the power grid, convert the levels of the received analog signals, and output the converted levels;
a plurality of analog-to-digital converters for converting analog signals output from the respective input converters into digital signals;
a plurality of Fourier transform calculation units that perform Fourier transform processing on the digital signals output from the respective analog-to-digital converters to calculate the amplitude and phase of each of the analog signals;
a correction calculation unit that executes a calculation to correct the amplitude value calculated by each of the Fourier transform calculation units with a first correction amount and a calculation to correct the phase calculated by each of the Fourier transform calculation units with a second correction amount;
a protection calculation unit that executes a protection calculation process for the protection target based on each calculation result of the correction calculation unit;
an analog-to-digital converter for a phase reference signal for converting the phase reference signal into a digital signal;
a phase reference signal Fourier transform calculation unit that performs the Fourier transform process on the digital signal output from the phase reference signal analog-to-digital converter to calculate an amplitude value and a phase of the phase reference signal and outputs each calculation result to the correction calculation unit;
The correction calculation unit is
a first correction amount calculated based on the amplitude value of the adjustment input signal among the calculation results of a specific Fourier transform calculation unit corresponding to the specific input converter among the multiple Fourier transform calculation units, and a second correction amount calculated based on the phase of the adjustment input signal among the calculation results of the specific Fourier transform calculation unit, on the condition that an adjustment input signal, which is an AC signal corresponding to the analog signal and has an amplitude value that changes sequentially in multiple steps from a low input amplitude minimum value to a rated input amplitude value of the analog signal in accordance with a sweep increment, is input to a specific input converter among the multiple input converters. 2. The digital protection relay device according to claim 1,
The correction calculation unit is
a gain correction amount indicating a ratio between an amplitude theoretical value defined in the phase reference signal and an amplitude value of the adjustment input signal calculated by the specific Fourier transform calculation unit is calculated as the first correction amount for each sweep increment, and a phase correction amount indicating a difference between the phase of the adjustment input signal calculated by the specific Fourier transform calculation unit and the phase of the phase reference signal calculated by the phase reference signal Fourier transform calculation unit is calculated as the second correction amount for each sweep increment. 2. The digital protection relay device according to claim 1,
The correction calculation unit is
a gain correction amount indicating a ratio between an average value of an amplitude theoretical value defined for the phase reference signal and an average value of the amplitude value of the adjustment input signal among the calculation results of the specific Fourier transform calculation unit is calculated as the first correction amount for each sweep increment, and a phase correction amount indicating a difference between an average value of the phase of the adjustment input signal among the calculation results of the specific Fourier transform calculation unit and a phase of the phase reference signal among the calculation results of the phase reference signal Fourier transform calculation unit is calculated as the second correction amount for each sweep increment. 2. The digital protection relay device according to claim 1,
The correction calculation unit is
calculating, for each sweep increment, a gain correction amount indicating a ratio between an amplitude theoretical value for each sweep increment defined in the phase reference signal and an amplitude value of the adjustment input signal among the calculation results of the specific Fourier transform calculation unit, and calculating, as the first correction amount, a gain correction amount calculated value by linear approximation using a least squares method based on the calculated gain correction amount for each sweep increment and the amplitude value of the adjustment input signal for each sweep increment;
a phase correction amount indicating a difference between a phase of the adjustment input signal among the calculation results of the specific Fourier transform calculation unit for each sweep increment and a phase of the phase reference signal among the calculation results of the phase reference signal Fourier transform calculation unit, and a phase correction amount calculated by linear approximation using the least squares method is calculated as the second correction amount based on the calculated phase correction amount for each sweep increment and an amplitude value of the adjustment input signal for each sweep increment. 5. The digital protection relay device according to claim 4,
The correction calculation unit is
When the analog signal is input to the input converter, on condition that the input amplitude of the analog signal is greater than an intermediate amplitude value that is intermediate between the low input amplitude minimum value and the rated input amplitude value, a first post-correction amplitude is calculated from the input amplitude of the analog signal and a rated gain correction amount, and a first post-correction phase is calculated from the input phase of the analog signal and a rated phase correction amount, correcting the amplitude value of the analog signal calculated by the Fourier transform calculation unit based on the calculated first post-correction amplitude, and correcting the phase of the analog signal calculated by the Fourier transform calculation unit based on the calculated first post-correction phase,
a second corrected amplitude is calculated from the input amplitude of the analog signal and the calculated gain correction amount value, and a second corrected phase is calculated from the input phase of the analog signal and the calculated phase correction amount value, on the condition that the input amplitude of the analog signal is between 0 and the intermediate amplitude value, correcting the amplitude value of the analog signal calculated by the Fourier transform calculation unit based on the calculated second corrected amplitude, and correcting the phase of the analog signal calculated by the Fourier transform calculation unit based on the calculated second corrected phase. 2. The digital protection relay device according to claim 1,
The correction calculation unit is
calculating, for each of the sweep increments, an input gain correction amount indicating a ratio between an amplitude theoretical value for each of the sweep increments defined in the phase reference signal and an amplitude value for each of the sweep increments which is an amplitude value of the adjustment input signal among the calculation results of the Fourier transform calculation unit, and recording the calculated input gain correction amount corresponding to each of the sweep increments in a gain correction lookup table as a first correction amount;
a phase lookup table for recording the calculated input phase correction amount corresponding to each sweep increment as the second correction amount, the phase correction amount being a phase of the adjustment input signal among the calculation results of the Fourier transform calculation unit, the phase correction amount indicating a difference between the phase of the adjustment input signal for each sweep increment and the phase of the phase reference signal among the calculation results of the phase reference signal Fourier transform calculation unit, and 7. The digital protection relay device according to claim 6,
The correction calculation unit is
when the analog signal whose amplitude value includes any one of the sweep increments is input to the input converter, an input gain correction amount corresponding to the sweep increment specified by the amplitude value of the analog signal is extracted from the gain correction lookup table, and the amplitude value of the analog signal calculated by the Fourier transform calculation unit is corrected based on the extracted input gain correction amount;
an input phase correction amount corresponding to the sweep increment specified by the amplitude value of the analog signal is extracted from the phase lookup table, and the phase of the analog signal calculated by the Fourier transform calculation unit is corrected based on the extracted input phase correction amount.

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